The present invention relates to an apparatus for displaying a remaining charge of a rechargeable battery and, more particularly, to an apparatus for displaying the remaining battery charge based on an accumulated discharge value which is computed from operating current and time of battery usage.
In a conventional apparatus, a storage section stores a fixed battery capacity value which is usually a standard full charge capacity of a rechargeable battery A controller computes an accumulated discharge value based on the operating current and time of usage by electrical equipment to which power is supplied from the rechargeable battery By comparing the stored battery capacity value with the accumulated discharge value, the remaining charge value of the battery can be obtained and displayed.
The conventional apparatus mentioned above has the following problems. Rechargeable batteries, such as a Ni-Cd alkaline battery, gradually decrease their full capacities as the number of recharging operations increases. Thus, the displayed charge value which is calculated using the stored, fixed battery capacity will differ from the actual remaining battery charge value. As a result, even though the displayed remaining charge value shows that the electrical equipment can still be operated by the battery, the equipment would suddenly stop for lack of battery energy.
Since different batteries have different capacities due to manufacturing variations, the standard capacity of batteries must be set to the minimum capacity among all batteries. This results in more charging operations, shortening the lives of batteries except for a battery having the minimum capacity.
Furthermore, the electrical equipment might use batteries having different capacities because of its limitation in size or in weight. In this case, the displayed remaining battery charge value which is calculated using the fixed battery capacity will also differ from the actual remaining battery charge value.